For shielding an electronic part which performs mechanical vibration (e.g., a piezoelectric element, a magnetostrictor or other movable part) from atmosphere and electrically connecting it to an external circuit to utilize the function thereof, generally, a so-called cavity encapsulation in which a space (vacuum or gas) is formed around the part is required instead of an encapsulation called molding, resin encapsulation or resin casting.
Conventionally, the cavity encapsulation is mainly carried out by means of hermetical sealing with a ceramic case, and recently, from the viewpoint of economic performances, the method of hermetical sealing with a resin material is also proposed in JP-A-9-148477, and the like.
As one example, FIGS. 4 and 5 show the outline of the structure of hermetical sealing with a conventional resin material, carried out by the present inventor. In these Figures, 1 indicates a resin wiring substrate, and an electronic part element 5 is spliced and fixed onto the resin wiring substrate 1 through a junction member (e.g., gold) 6. The electronic part element 5 is connected to an outside with a conductor on the wiring substrate 1 and via a through hole 4 formed in the wiring substrate 1 as an electrically conductive through hole. 2 indicates a resin frame substrate, a space necessary for housing the electronic part element 5 is made, a resin cover substrate 3 is placed thereon, and the wiring substrate 1 and the frame substrate 2, and the frame substrate 2 and the cover substrate 3, are hermetically bonded to each other with an adhesive. Then, the resultant set is cut in cutting positions Z to obtain individual electronic parts as shown in FIG. 5. With the conductor on the wiring substrate 1, the through hole 4 is connected to the electronic part element 5 housed in a cavity 7 surrounded by the wiring substrate 1, the frame substrate 2 and the cover substrate 3, whereby a surface-mounting electronic part using a semi-cylindrically cut through hole surface 4a as a side electrode for external connection can be constituted, and the function of the electronic part element 5 housed inside can be worked by connecting the through hole surface 4a to an external circuit.
FIGS. 6 and 7 show enlarged views of a through hole portion of the hermetical sealing structure formed of a resin material shown in FIGS. 4 and 5. In the through hole 4, a Cu plating layer 12 is coated on an inner circumferential surface by Cu plating, and an Au plating layer 13 as an uppermost layer is coated thereon through an Ni plating layer (not shown) by Au plating, for the purpose of electrically connecting conductors 10 and 11 (e.g., Cu copper foil patterns attached to the substrate) on upper and lower surfaces of the resin wiring substrate 1.
The purpose in the Au plating is to form a chemically stable surface so that the soldering performance is not degraded when the above surface mounting electronic part is exposed to atmosphere for a long period of time, since the inner surface of the through hole 4 and the external connection surface (lower side in Figure) of the wiring substrate 1 constitute soldering surfaces when the part is used. In this case, land pads l0a and 11a are provided on both sides of the through hole 4 for easy plating on the interior of the through hole and securing the reliability of connection to the patterns on the wiring substrate 1. These land pads lOa and 11a are constituted as annular portions integrally formed on end portions of the conductors 10 and 11 on the upper and lower surfaces of the resin wiring substrate 1 so as to surround the entire circumferences of peripheries of the above through hole 4. Further, the above Cu plating layer 12 to the above Au plating layer 13 as an uppermost layer are laminate-formed by the above plating procedures.
In FIGS. 6 and 7, those portions which are the same as those in FIGS. 4 and 5 are indicated by the same symbols.